1TB "missing".

[thedoginthewok]

Hello,

I've installed NAS4Free today and set up a RAIDZ1.

I have 8 WD Red 3TB Hard drives. According to this calculator

http://www.servethehome.com/raid-calculator/

It should give me 19.1 TB of usable space:

RAID-Z
*Raw Storage: 24.0 TB / 24000.0 GB
*Usable Storage: 19.1 TB / 19557.8 GB
RAID-Z uses one disk for Parity much like RAID5 and requires at least three drives to be used.


*Usable storage is the actual post-format amount where kilo = 1024, not 1000

This is what the NAS4Free webgui shows me:


Where did the Terabyte go?

[Lee Sharp]

Some space is also used for the intent log and snapshots, even if you have not yet taken any snapshots.

[thedoginthewok]

Can I read something more about "some" space?

I just want to know how the drives are utilized. Is 1TB a high amount for an intent log and snapshots?

[b0ssman]

the calculator does not take into account the zfs overhead for checksums, logs etc..

the calculated size for raid5 and raidz1 are identical.

what you are seeing in nas4free is the correct value.

[raulfg3]

I remember that UFS formated drives have 8% in size overhead to permit root login in case of filesystem full, perhaps ZFS have simmilar % overhead for the same reason, but I do not confirm this info.

[substr]

There should definitely be some 'missing.' Whether 1TB is the right number, I don't know.

There isn't anything 'wrong' though, I think you can be confident in that.

It wouldn't be possible to actually store 19TB on the array, because metadata is going to consume some of the space, and if you've properly selected 4K/advanced format when you created the pool, there will also be some space lost in padding. 7 data drives is not equal to 2/4/8, so the blocks are going to be split in uneven multiples of 4K. This will lead to 'missing' space, but I think it is lost 'along the way,' and can't be calculated in advance(the block size determines the % of padding loss).

[thedoginthewok]

Okay. Thanks to you all for the answers.